As design rule decreases due to the trend towards large scale integration of semiconductor devices, and thereby the line width of electronic devices constituting semiconductor devices narrows, small-sized and high performance electronic equipment has been achieved owing to a larger number of transistors per unit area, which causes, however, that the ratio of heat emission of a semiconductor device per unit area increases. The increase of the rate of heat emission deteriorates the performance of semiconductor devices and lessens the life expectancy thereof, and eventually decreases the reliability of a system adopting semiconductor devices. Particularly in semiconductor devices, parameters are too easily affected by operation temperatures, and thereby that further deteriorates properties of integrated circuits.
In response to the increase of the rate of heat emission, cooling technologies have been developed such as fin-fan, peltier, water-jet, immersion, heat pipe type coolers, etc., which are generally known.
The fin-fan type cooler which compulsorily cools devices using fins and/or fans has been used for tens of years, but has some defects such as noise, vibration, and low cooling efficiency compared to its large volume. Although the peltier type cooler doesn't make noise or vibration, it has a problem that it requires too many heat dissipation devices at its hot junction needing large driving power in accordance with the law of conservation of energy. The water-jet type cooler goes mainstream in cooling device research because of its efficiency, but its structure is complicated due to the use of a thin film pump driven by an external power supply, and it is significantly affected by gravity, as well as a problem that it is difficult to achieve robust design when applied to personal mobile electronic equipment.
Due to above problems, the heat pipe type cooler is recently widely applied in various shapes as a compact type cooling device together with the fin-fan type cooler because its advantages that it is simple in structure and easily manufactured. That is, as shown in FIG. 1, a conventional cooling device 10 combining both heat pipe and fin-fan includes a heat pipe 12 contacting a heat source 20 at one end thereof, a plurality of fins 14 being disposed at the other end of the heat pipe 12, and a fan 16 being disposed near the fins 14, whereby the heat absorbed from the heat source 20 is dissipated by the fins 14.
In the cooling device 10 using such heat pipe, since the flowing directions of gas and liquid are opposite each other, it dries out when a large quantity of heat is applied to the heat pipe, because the liquid returning to an evaporation section from a condensation section is sucked again into a gas transfer section due to the speed of the gas generated, so that it eventually fails to return to the evaporation section. In addition, there is a problem that its installation location is significantly restricted because the evaporated refrigerant is transferred depending on the difference between buoyancy and pressure in the heat pipe, and the liquefied refrigerant in the heat pipe depends on gravity due to the structure and size of the medium of the returning section.
Further, since the amount of heat produced by a highly integrated semiconductor device such as an up-to-date CPU is so large that the conventional cooling device cannot deal with the heat, even the cooling device 10 combining heat pipe and fin-fan can manage to cool only when equipped with three or four of the heat pipes 12 and two or more of the fans 16. If the elements increase as above, the size of the device becomes too large, and besides noise and power consumption by lots of the fans 16 also increase considerably, so that it isn't useful any more. The disadvantage of the convention heat pipe type cooler as above is that the loss of heat transfer at the fins themselves rapidly drops in comparison to the heat transfer at the phase transition medium, because it has to transfer heat through fins of large area even though utilizing phase transition of fluid.